Telephone system



J1me 1940- s B. WILLIAMS TELEPHONE SYSTEM 2 Shes tS-SIIGGC l n I i O 9 IQ N UK Filed July 8, 193

A Hg? IN [/5 N TOR By 5.8. W/LL/AMS MW m A T TOR/VEV June 25, 1940. s B.w LL AMs 2,205,551

' TELEPHONE SYSTEM Filed July 8, 1939 2 Sheets-Sheet 2 CONS TAN 7"CURRENT SOURCE /N l EN TOR -S. B. WILLIAMS A TTORNE V Patented June 25,1940 UNITED STATES PATENT OFFICE TELEPHONEv SYSTEM Samuel B. Williams,Brooklyn, N. Y., assignor to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application July 8, 1939,Serial No. 283,352

6 Claims.

This invention relates to telephone systems and particularly toautomatic systems in which the subscribers are charged for the servicerendered by means of message registers.

The objects of the invention are to prevent the operation of the messageregisters from interfering with the functions of the switchingequipment; to insure against false operation of the message registers inthe event that unstandard conditions occur in the circuits associatedtherewith; to test the message register operating circuits to determinethat they are in proper condition before applying operating currentsthereto; and to secure other improvements in systems of this character.

A feature of the invention is a system in which a single controlconductor is utilized for controlling the hunting movement of the linefinder that seizes the subscribers line and for applying operatingcurrent to the subscribers message register, in which the test relay ofthe line finder, which energizes to stop the movement of the line finderwhen it seizes the terminals of the calling line, is permitted tooperate in case the finder encounters the terminals of a line on whichmessage registration is taking place, and in which the test relay sooperating prepares a circuit, depending upon the busy condition of theline encountered, to maintain the continued movement of the finder overthe busy line thus encountered. This feature has special utility inconnection with party line systems where two message registers areconnected through polarizing devices, such as rectifiers, to thecombined message register and hunting lead of the line finder switch.The presence of these rectifying devices in this lead increases theresistance thereof and raises the potential on the multiple terminals ofthe lead in the line finder switch. If, therefore, a finder encountersthe multiple terminals of this lead at the instant message registrationis taking place, the potential thereon is sufficient to operate thetestrelay of the finder. This operation would, except for 4 theprovisions above explained, result in the trical connection with eachother. If these operating conductors are crossed the current suppliedover the common operating conductor from the constant current source isinsufficient to operate both registers.

Another feature of the invention is a testing arrangement in which atest is made automatically to determine whether the message registerlead of any particular line is in proper condition before operatingcurrent is applied thereto. If the operating lead is in engagementaccidentally with the corresponding lead of some other line, a testrelay operates and serves to withhold the application of the registeroperating current and to give an alarm.

These and other features and advantages of the present invention will bedescribed more fully in the following detailed specification.

In the drawings accompanying the specification Figs. 1 and 2 illustratean automatic telephone system partly in diagrammatic manner and partlyin detail.

Fig. 1 shows a two-party subscribers line appearing in a line finderswitch together with a portion of one of the links comprising a linefinder and a district selector switch; and

Fig. 2 shows the remainder of the finder-district link circuit togetherwith the succeeding switches used in establishing a connection to acalled line.

The subscribers line I, having two substations thereon, appears in theterminals of line finder switches, such as switches F and F-l. Each ofthe finder switches is paired with an individual district selectorswitch comprising a link circuit. For example, the finder F is pairedwiththe district selector S, and the relays and other equipmentassociated with these switches constitute the link circuit. In additionto the various relays of the link. circuit a sequence switch is providedhaving numerous circuit-controlling contact springs which advancethrough successive' positions for performing the necessary switchingoperations.

The district selector switches have access to finder switch seizes thecalling line. The fourth brush of the finder switch has two functions.One of these is to extend the test or hunting circuit whereby the finderis able to determine which line is calling. The second function is tofurnish a circuit for the operation of the subscribers messageregisters. Since it is necessary to discriminate between two messageregisters, where the subscribers line has two parties thereon, theoperation of one or the other of these registers must be performed overa single circuit, namely the one extending through the fourth brush ofthe finder switch. More specifically, the brushes 2 and 3 of finder Fare the ones that extend the talking circuit. Brush 4 is the sleevebrush, which completes the operating circuit for the cutoff relay 5. Thefourth brush 6 is the one that controls the hunting operation and alsothe message register operating circuit.

The discrimination between the message registers i and 8 of the partyline I is obtained by means of rectifying devices 9 and ii). Theregisters T and 8 are connected through a resistance l i and a contactof the line relay l2 to the single hunting and message register controlconductor [3. By poling the rectifiers 9 and It oppositely it ispossible to select the register 7 by applying current of one polarity tothe conductor l3 and to select the other register by applying current ofthe opposite polarity.

Discrimination between the two substations i4 and I is made by means ofa party test in the link circuit. This test is made at the proper stagein the progress of the call to determine whether a ground connectionexists on the line. If the party at substation It is calling, a groundconnection is applied through the switchhook contacts and the ringer Itto the tip conductor is of the line I, whereas if the party atsubstation E5 is. calling no ground connection is present.

While the invention is not necessarily limited to any particular kind ofsystem, it has been illustrated in connection with an automatic systememploying switches of the panel type. In view of their well-knowncharacter the structure of these switches, such as the line finders Fand Fl and the selectors S, 8-! and S--2,

has been largely omitted from the disclosure. Also the controllingcircuits associated with the line finder and district selector switchesF and S have been abbreviated as far as possible in order to facilitatean understanding of the present invention. However, reference may be hadto the following patents for an understanding of the detailed circuitsand operation of systems of the type to which this invention isapplicable: Taggart et al. 1,513,351 of October 28, 1924, Irvine1,541,356 of June 9, 1925, and Johnson et al. 1,859,924. of May 24,1932. In particular, the patent to Taggart et a1. and the patent toIrvine disclose a system of this character in which identification testsare made on two-party lines for the purpose of message registration.

The rectifying devices 9 and I0 may be of any suitable type, such as thewell-known copperoxide rectifier.

The operation of the system will now be described, and to this end itmay be assumed that the subscriber at station M wishes to converse withthe subscriber of line H. When the calling party removes his receiverfrom the switchhook, a circuit is closed from battery through the linerelay I 2, left contact of cutofi relay 5, over the line conductor I8,through the closed loop at substation l4 and returning over the lineconductor I9 to ground through the right back contact of relay 5. Relayl2 at its right front contact applies battery potential to the huntinglead I3. At its left contact relay l2 closes a circuit from ground overthe start conductor through closed contacts of sequence switch cam 2|,conductor 22 through the winding of the line finder relay 23 to batteryand ground.

The cam 2! is one of a plurality of contactmaking elements controlled bythe sequence switch magnet 24, which advances the cams through asuccession of positions to cause the opening and closing of the variouscontacts for circuit controlling purposes. It may be assumed that thesequence switch 24 is standing in position 2 at this time awaiting theseizure of the link, to which it is individual, comprising the finder Fand district selector 8.. In position I the sequence switch serves inthe well-known manner to control the allotment of the link. In positionI of the sequence switch the link comprising the line finder F andselector S awaits the preselection by a sender link circuit, not

shown. As soon as the preselection takes place the sequence switch 24advances into position 2 where, as stated, it awaits a call. The purposeof the sender selector link, with which we are not particularlyconcerned in connection with this invention, is to associate thesubscribers line, after it has been seized by the line finder F, with anidle central office register sender.

Relay 23 in operating locks in a circuit from battery through itswinding and contact, contacts of sequence switch cam 25, normal contactsof relay 35 to ground through the normal commutator segment 3| of thefinder switch. The segment 3| has ground potential connected thereto inall positions of the finder F except the extreme uppermost position ofthe brushes. Relay 23 in operating also closes the driving circuit forthe line finder F. This circuit may be traced from battery through thewinding of the up-drive magnet 26, inner lower contact of relay 23,contacts of sequence switch cam 21,

middle lower front contact of relay 23, left contact of sequence switchcam 28 to ground at sequence switch cam 29. The magnet 26 causes thebrushes 2, 3, 4 and 6 of the line finder F to move upwardly over theterminal bank in search of the terminals of the calling line I. As thefinder moves upward the hunting brush 6 passes over the huntingterminals of the subscribers lines, and the test relay 38 tests theseterminals for the presence of battery potential, indicating the callingcondition of a line. As soon as the brushes 2, 3, 4 and 5 encounter theterminals of the line I the test relay 30 operates in a circuit fromground through the contactsof sequence switch cam 32, winding of relay30, conductor 33, brush 6, terminal 34, lead l3, front contact of relayl2 to battery. Relay 30 opens the holding circuit of relay 23. Relay 23remains energized until the brush engages an insulating segment of thecentering commutator 36. Thereupon relay 23 releases to open the circuitof the power magnet 26 and bring the line finder F to rest centered onthe terminals of the calling line I. While the sequence switch is inpositions 2 and 3 the line is held busy by means of a circuit fromground over cam 29, cam I M, back contacts of relay 23 to conductor 40.

Relay 23 on releasing closes a circuit for driving the sequence switch24 out of position 2. This circuit may be traced from battery throughthe winding of the sequence switch magnet 24, contact cam 31, uppercontacts of cam 38, through the contacts of relay 39, which relay is inan operated condition at this time, middle lower back contacts of relay23, left contacts of cam 28 to ground at cam 29. In position3 of thesequence switch, and from there on to position 17 A a circuit ismaintained over the sleeve conductor for operating and holding thecutofi relay energized and for placing a busy condition on the multiplesleeve terminals accessible to other find-er switches. The busy sleevecircuit may be traced from ground through the left contacts of cam 29,conductor 4|], resistance 4!, brush 4, terminal 42, conductor 43,winding of the cutoff relay 5 to battery. This ground potential alsoappears on the multiple sleeve terminal 44 in the line finder switch FIand similarly on the terminals of other line finder switches havingaccess to this line. Relay 5 operates and releases the line relay 12 toremove ground from the start conductor 20 and also to remove callingbattery potential from the hunting lead 13.

In the manner well known in the art and disclosed in detail in theTaggart et al., Irvine, and Johnson et al. patents, above mentioned, theline finder-district link progresses to the point where the callingsubscribers line is extended by Way of sequence switch cams 45 and 46and conductors 47 and 48 to an idle register sender, not shown; thesubscriber at the calling station manipulates his dial 49 to set theregisters of the sender in accordance with the designation of the calledline H; the fundamental circuits are prepared, and the selectors S, Sland 8-2 are operated under the control of the register sender to extendthe connection to the called line. During these proceedings the sequenceswitch 24 associated with the link is advanced from position toposition, passing into position ll following the extenson of theconnection to the called line.

As the sequence switch 24 reaches position II a test is made of thecalling line I to determine which one of the two stations has initiatedthe call. In preparation for this test a circuit is closed from batterythrough the winding of relay 50, conductor 5|, contacts of sequenceswitch cam 52 to ground. Relay 50 operates and extends the groundedconductor 5| through its front contact, over conductor 53 through thewinding of relay 54 to battery. Relay 54 operates in this circuit andconnects the test relay 55 to both talking conductors 56 and 51 of thelink. Relay 55, therefore, is connected by way of finder brushes 2 and 3to the talking conductors l8 and IQ of the line I. Since the party atstation l4 has his receiver off the hook, the grounded ringer I6 isconnected through the upper switchhook contacts to both line conductorsl8 and IQ. Test relay 55 operates in this circuit and closes a circuitfrom ground over its front contacts, conductor 59, outer left contact ofrelay 60, conductor 6| through the Winding of relay 52 to battery. Relay62 operates and locks through its upper front contact to ground throughsequence switch cam 63. Relay 52 remains locked through position 18 ofsequence switch 24 to record the fact that the test revealed thepresence of a ground potential on the calling line, indicating that thecall was initiated by the party at station 14. As soon following thearrival of the sequence switch in position H as the constantly-driveninterrupter 64 operates its right contacts a circuit is completed frombattery through the left winding of relay 65, right contacts ofinterrupter 64, contacts of cam 52 to ground. Relay 65 operates andlooks through its inner left contact to ground on conductor 5|. As soonthereafter as interrupter 54 closes its left contacts a circuit iscompleted from the grounded conductor 5|, left contacts of saidinterrupter, outer left front contact of relay 65, conductor 65, middlelower contact of relay 54', winding of relay 23 to battery. Relay 23operates and closes a circuit for driving the sequence switch out ofposition II. This circuit may be traced from battery through the magnet24 of the sequence switch cam 31, left contact of cam 38, lower frontcontact of relay 23, through the contacts of cams 28 and 29 to ground.As the sequence switch passes out of position H 4 it opens the leftcontacts of cam 52, and ground is removed from conductor 5| to permitthe release of relays 50, 54, 55 and 65. The release of relay 54 opensthe operating circuit of relay 23.

In subsequent positions of the sequence switch, such as positions l3 andI4, the talking circuit is completed, and for conversation between thecalling and called subscribers. At the time the called subscriberanswers the supervisory relay 61 operates, closing a circuit from groundthrough the front contact of said relay, conductor 68,,contacts ofsequence switch cam '69 to conductor 70. As soon thereafter as thepowerdriven interrupter H closes its left contacts the conductor isextended through the right winding of relay 65 to battery and ground.Relay 65 operates and locks through its inner right contact to thegrounded conductor 10. When thereafter interrupter H next closes itsright contacts the grounded conductor 10 is extended by way of saidright contacts, outer right front contacts of relay 65, through thewinding of relay 60 to battery and ground. Relay 60 operates and locksthrough its inner left contact, upper left contact of sequence switchcam 12 to ground over conductor 13, Thus the relay 60 operates to recordthe fact that the called subscriber has answered.

After conversation has ceased and the calling subscriber has replacedhis receiver on the switchhook, the sequence switch 24 is driven out ofthe talking position and into position l5. As the sequence switch entersposition I5, the relay 55 is reoperated and, in its operated condition,is applied to the calling line to make a second test to determinewhether the line is free from ground potentials. The operating circuitof the relay may be traced from battery through the winding thereof,conductor 14, middle left contact of relay 60, lower left contacts ofsequence switch cam 12 to the grounded conductor '33.

Relay 55 operates relay 50 in a circuit from ground through the contactof relay 55, conductor 59, outer left front contact of relay 6!),conductor 75, conductor 5i, thence through the winding of relay 5!] tobattery. Relay 5!] operates and extends the grounded conductor 5|through its closed contact to conductor 53, operating relay 54. Relay 54connects the winding of the operated test relay 55 to the tip and ringconductors of the subscribers line I to determine whether relay 55 willhold after its energizing circuit has been opened; or, in other Words,to determine whether there is a ground connection on the subscribersline after he has replaced his receiver to remove the groundedconnection at the ringer l6. Relay 54 in operating also closes a circuitfrom battery through the winding of relay 23, lower contact of relay 54,conductor 16, upper, left contacts of cam 12 to ground over conductcrI3. Relay 23 operates and completes the circuit above traced for drivingthe sequence switch 24 out of position I5 and into position I6. As thesequence switch leaves position I5 the lower left contact of cam I2opens the energizing circuit of the test relay 55, leaving this relaydependent for its maintained energization upon he circuit closed throughthe contacts of relay 54 to the line conductors. If the line has groundpotential thereon, relay 55 is maintained energized and in turn holdsrelays Ell and 54 to prevent the sequence switch from advancing further.Relay 54 energizes the time measuring and alarm device Eli, and, afteran interval has expired, this device gives an alarm to indicate thepresence of an abnormal condition. If the subscribers line is in itsnormal condition and has no ground connection thereon, relay 55immediately releases. The release of relay 55 permits the release ofrelays 59 and 54, provided the test relay II, which will be describedpresently, has not operated at this time to indicate an unstandardcondition on the message register operating conductor l3.

In positions I5 and I5 of the sequence switch a second test is made,simultaneously with the testing of the subscriber's line, to determinewhether the hunting and message register operating lead 5 3 is inaccidental connection with the corresponding lead of some individualsubscribers line. If two of these leads are crossed, the danger is thatthe application of metering potential to one of them will cause thefalse operation of the register on the other line.

The test for the crossed condition of the operating leads is made by thetest relay TI. This relay is differential, and its windings and theassociated resistance elements constitute a bridge circuit in which theoperating winding of the relay is insuhicient to attract the relaysarmature if the lead IE to which the test relay is applied is instandard condition. However, the test relay will operate in case theresistance of the lead I3 is abnormally low due to a parallel path toground through the message register of an individual subscribers line.When relay 50 operates following the movement of the sequence switchinto position I5, the conductor i8, connected to the test relay IT, isextended through contacts of cam I9, conductor 8!], closed contact ofrelay 55, conductor 33, brush 6, terminal 34, conductor l3, back contactof relay I2, resistance H, to the conductor BI common to the registers iand ii. Also the operation of relay 50 connects the conductor 82 toground. With these circuits closed an electrical bridge arrangement isestablished in which three of the arms are formed respectively by theresistances 83, 84 and 85, in which the fourth arm is formed by theresistance II and the register 8, in which the left winding of relay I!is connected across the balance points of the bridge, and in which thebattery and the right winding of relay Ill and the resistance 88 areconnected in series with the bridge. The left winding is differential tothe right winding and receives suflicient current in the opposingdirection to prevent the relay from operating when only the conductor I3of one line is included in the fourth. arm of the bridge.

Should the conductor l3 of the party line be accidentally crossed withthe corresponding conductor of an individual line, the combinedresistance would be sufficiently low to cause the operation of thedifierential relay T. to prevent the subsequent application of meteringpotential to the conductor 93. It follows, of course, that the parallelpaths present when the conductors [3 of two lines are crossed result ina lowering of the resistance connected in series with conductor 33. Andin the case assumed, namely, when a two-party line is crossed with anindividual line, the combined resistance is so lowered that relay 71operates. This is true by reason of the fact that the conductor I3 of anindividual line is substantially lower in resistance since it does notinclude a rectifier nor the series resistance II. Should the conductorsI3 of two different party lines become crossed, the combined resistancewould be somewhat higher than the ease assumed, and it might be that thetest relay would not be adjusted to detect this condition. In such acase, however, false operation of the registers on the party lines isprevented by limiting the current supply. This feature Will be explainedlater.

Assuming, therefore, that conductor #3 of line I is crossed with thecorresponding conductor of an individual line, relay 'I'I operates andlocks in a circuit through its windings in series and its inner lowercontact to ground over conductor 89. In operating, relay 'I'I closes agrounded circuit by way of its outermost contact, conductor 99 andthence through the windings of relays 54 and Eli to battery, holdingthese relays energized after the sequence switch has passed out ofposition Ita to release relay 55 in the event the tip and ringconductors of the subscribers line are in normal condition. Themaintained energization of relay 54 prevents the sequence switch fromadvancing out of position i6, and a circuit is closed from groundthrough the uppermost contact of relay 54 to the timing and alarmcircuit 9i. After a measured interval has expired the circuit 9i givesthe necessary alarm to call attention to the fact that the equipment hasencountered trouble.

If, however, the subscribers line I is free from ground potential, andif the message register operating lead I3 is not in contact with thecorresponding lead of an individual subscriber's line, when the sequenceswitch moves into position l5 and into position I6 as above described,the test relay 55 releases, and the test relay 1'! fails to operate.Consequently, relays 50 and 54 release as the sequence switch 'moves outof position I5 4 and into position I5. leases the relay 23, and acircuit is closed from battery through the winding of sequence svitchmagnet 24, contacts of cam 31, contacts of cam 92, back contacts ofrelay 23 and thence to ground through the contacts of cams 28 and 29.The

sequence switch moves out of position I6, through position II and intoposition I8.

In position I! metering current is applied to the conductor I3 tooperate the register individual to the calling party on the line I. Themetering current is supplied from the current supply device 93 and thecircuit therefor may be traced from the positive pole of said deviceover conductor 94, through the lower front contact of operated relay 62,conductor 95, right front contact of relay 6|], conductor 96, contactsof cam 91, thence over conductor 33, brush 6, and terminal 34 toconductor l3 through the back contact of relay I2, resistance I I,conductor 8i, through the rectifier 9 and the winding of register I toground and returning through the inner lower front contact of relay 62and conductor 93 to the negative pole of the supply circuit 93. Sincethe current flowing in this circuit passes only through the rectifier 9,only the mes Relay 56 resage register I will operate, charging thefc allto the subscriber of station I 4.

As the sequence switch moves into position I8 the necessary releasecircuits are closed for restoring the line finder switch F .and theother switches to their normal position. The sequence switchthen'advances into position I; where it awaits allotment. i

When the other party on the line I, namely, the party at station I5,makes a call, the operation of the system is substantially the same,except that the test of the line by the relay 55 fails to find a groundpotential thereon. There being no ground potential on the line when theparty at station l5 calls, relay 55 does not operate in position II ofthe sequence switch, and

relay 62 consequently remains deenergiz'ed. When, later, the sequenceswitch is in position I I, the metering circuit is closed, and currentof the opposite polarity flows thereover to operate the register 8individual to the station I5. This circuit may be traced from thenegative pole of the constant current supply device 93, conductor 98,lowermost back contact of relay 62, thence over conductor 95 as abovetracedtothe common conductor 8| through the rectifier I0, winding ofregister 8 to ground and from ground through the inner lower backcontact of relay 62, conductor 94 to the positive pole of the currentsupply device 93.

It has already been explained how the system is guarded against possiblefalse operation of a message register when the conductor I3 of a partyline is in accidental connection with the corresponding conductor of anindividual subscribers line. This safeguard is afiorded by the testrelay 1'! which does not operate in circuit with the normal resistanceof the lead I3 of. a party line but does operate in circuit with therelatively low combined resistance of lead I3 of a party line and thecorresponding lead (crossed therewith) of an individual subscribersline. It is also desirable, of course, to prevent false operation in theevent that the leads I3 of twopartylines should become accidentallycrossed. Since both of these leads contain the resistance element II andthe rectifier element, the combined resistance is substantially greaterthan that encountered when a party line and an individual linearecrossed. In such a case it might be .difficult for the relay TI todistinguish between the resistance of a single party line lead and thecombined re,- sistances ofv two party line leads. It ispossib-le,however, to prevent the false operation of .the registers by limitingthe amount of current flowing over the message register operatingcircuit to a value which is insuflicient to operate either of theregisters of the two party lines whose leads have become crossed. Thisis accomplished by means of the constant supply device 93, whichconverts alternating current into direct current and supplies it to theoutput conductors 94 and 98. For this purpose alternating current issupplied over conductors 99 and IE0 to the constant current rectifier93.

Thus if the conductors I 3 of two party lines are crossed at the momentmetering current is applied over conductor 95 to the conductor I3 of theline against which it is desired to assess a call, the loweredresistance, which would otherwise tend to draw the greater currentrequired for operating both registers is without efiect. The constantcurrent device 93 maintains its output current at a constant valueregardless of. the increased load, and this value is insufficient tocurrent rectifying device suitable for use in this system is shown inthe patent to Bodde, No. 1,298,443 of March 25, 1919.

It will be recalled from the foregoing .descrip' tion that the singlelead I3 is used for the hunt ing operation of the line finder and laterfor, the message register operation. Since each line is multipled beforea number of final switches, it is possible for a moving finder switch totest the lead I 3 of a line in the hunting operation at the same instantthat another finder, whichlhasalready seized said line for aconversational con 'nection, is applying message register operatingcurrent to the same lead. Under these conditions the resistance includedin the lead I3 may be suificient to raise the potential of the huntingterminal to a point where a test relay in the hunting finder operates.Inasmuch as the oper ation of the test relay normally indicates that thefinder has found the calling line it is seeking, it is necessary toprovide meansfor ignoring the operation of the test relay under theconditions above mentioned. Assume, for. example, thatthe subscribersline, I has made a call, that the con,- nection was established by Wayof the line finder switch FI, that conversation is over, and thatmessage register operating current is being'applied by way of conductorI01, brush I08, terminal I09 to the lead, I3 to the line I. Assume alsothat. the finder switch F, which is seeking some other calling line,encounters the terminals of line I at this particular instant. It willberecalled thatduring the hunting operation of the finder switch F,sequence switch 24 is in position 2 and the'rela'y 23 is operated andlocked through its inner upper contact, contacts of cam.25 to groundthrough the commutator, 3|. When the brush 6 of the finder F encountersthe terminal 34, having the message register operating potentialthereon, current flows by way of the brush 6 and conductor 33 throughthe winding of relay 30,:contact cam 32 to ground. This-operates therelay 30,,but relay 23, which normally would .release at this time toterminate the hunting movement of the finder, is held in another circuitto insure the continued movement of the finder F past the line I and insearch for theother calling line. The holding circuit for relay 23 may'be traced from battery through the winding and inner upper contactthereof, contacts of; cam 25,,

make-before-break contacts of relay. 3EI', conduc- 1 releases andrecloses the normal holding circuit of relay 23 through the commutator3|.

What is claimed is:

1'. In a telephone system, line finder switches, subscribers linesappearing in the multiple terminals of said finders, each line having amessage register, a combined test and register operating conductor foreach line appearing in the test terminals of said finders, meansassociated with a finder that has seized a line to render the seizedline busy and to apply a source of register-operating potential to saidtest terminals to operate the register or". said seized line, means forapplying a calling potential to the test terminals of a calling line andfor initiating the hunting movement of one of said finders, test meansoperative in response to said calling potential to stop the huntingfinder on the terminals of the calling line and also operative inresponse to said register-operating potential in case the hunting finderengages said seized line at the moment registeroperating potential ispresent on the test terminals thereof, and means for preventing thehunting finder from stopping on said seized line when the said findertest means is operated by said register-operating potential.

2. In a telephone system, line finder switches, subscribers linesappearing in the multiple terminal sets in said switches, each terminalset including a sleeve terminal and a hunting terminal, messageregisters for said lines, means responsive to a call on one of saidlines for applying a calling potential to the hunting terminal thereofand for initiating the hunting movement of a line finder switch, a testrelay in the line finder responsive to the calling potential on saidhunting terminal for causing the finder to seize the terminals of thecalling line, means controlled by the operated finder switch for placinga busy potential on the sleeve terminal of the seized line, meanscontrolled by the operated finder switch for applying aregister-operating potential to the hunting terminal of the seized lineto operate the associated message register, means responsive to a callon a second line for initiating the hunting movement of a second finderswitch, a test relay in the second finder switch responsive to thecalling potential on the hunting terminal of a calling line for seizingthe same and also responsive to the register-operating potential on thehunting terminal of said firstmentioned line in case said second finderencounters the hunting terminal of said first line at the moment thesaid register-operating potential is present thereon, and meansassociated with said second finder switch for rendering its test relayineffective to stop said second finder on the terminals of said firstline and for causing said second finder to continue its movement insearch of said second-mentioned calling line.

3. In a telephone system, subscribers lines having message registers, acontrol conductor for each of said lines for operating the messageregister thereof, a common current supply conductor connectable to thecontrol conductor of any calling line, and a source of constantintensity current for operating a desired register over a circuitincluding the common supply conductor and the control conductorassociated with the desired register, the current supplied from saidsource being sufficient to operate the register of any one of said linesbut insuificient to operate the registers of two lines in case thecontrol conductors of said lines are accidentally in contact with eachother.

4. In a telephone system, subscribers lines having individual messageregisters, control circuits individual to said lines for operating therespective registers, a line finder switch for seizing a calling line, acommon supply conductor connectable by said finder switch to the controlconductor of the seized line, and a constant current supply sourceassociated with said finder switch for supplying operating current tothe register of the seized line over a circuit including the commonsupply conductor and the individual control conductor, the current fromsaid source being independent of the resistance of said circuit andsufiicient to operate a single register but insuflicient to operate tworegisters in case the control conductors of two lines are in contactwith each other.

5. In a telephone system, subscribers lines having message registers,message register conductors for operating said registers, a selectiveswitch for seizing a calling line, a common operating conductorconnectable through said switch to the message register conductor of thecalling line, resistances in said message register conductors, a testrelay connectable to said common conductor for testing the resistance inseries therewith and operative if the message register conductor of thecalling line is in contact with that of a second line, a source ofcurrent applicable to said common conductor to operate the calling linemessage register, and means controlled by said test relay to withholdthe application of said source.

6. In a telephone system, party lines, individual lines, messageregisters for said lines, control conductors individual to said linesfor operating the associated message registers, resistance elements inthe control conductors of said party lines, a finder switch for seizinga calling line, a common supply circuit connectable through said switchto the control conductor of the calling line, a test relay connectableto said common conductor for testing the resistance in series therewithand operative if the control conductor of the calling line is in contactwith that of a second line, a source of current applicable to saidcommon supply circuit to operate the calling line message register, andmeans controlled by said test relay to withhold the application of saidsource.

SAMUEL B. WILLIAMS.

